I concur with what mbtjc stated. I suspect you should have no more/no less effort maintaining a euro 500SEL than I do with my 85 US version ( I have the euro lights because it is the right thing to do
One caveat. You stated it still has a current German inspection. Does that mean it is a current transplant, and has not yet been licensed in the US? If so, depending on where you live you could have some hoops to go through local agencies to get emissions/safety inspections prior to vehicle licensing.
As far as engine goes - remember this was the flagship version for MB in their own back yard.
Can you say autobahn